I haven't personally used File::NFSLock, but from what I read in the docs, if you request an exclusive lock, only one process will get the lock. The other process may block until the lock becomes free, or until a specified time has passed. If the time passes before the lock becomes free, the return lock will be undef.

The example included in the module documentation,seems understandable.

However not having used this module, I can only assume that it works as advertised. Are you aware of anything to the contrary?